What is the Schedule Performance Index?

In project management, getting an early indication of problems is the silver bullet that allows the project manager to correct the problems before they start.

TheSchedule Performance Index, usually abbreviated as SPI, is one of the fundamental outputs of Earned Value Management. It tells the project manager how far ahead or behind the project is at the point of analysis (usually right now).

Formula

SPI = EV / PV

Where:

SPI = Schedule Performance Index

EV = Earned Value (dollars, euros, etc.)

PV = Planned Value (dollars, euros, etc.)

Interpretation of Results

If SPI is less than 1, the task is behind schedule.

If SPI is 1, the task is on schedule

If SPI is greater than 1, the task is ahead of schedule.

For example,

SPI = 0 means the project work has not started.

SPI = 0.5 means the project has performed half the work it was supposed to at this point.

SPI = 1.0 means the project is on schedule.

SPI = 2.0 means the project has performed twice the work it was supposed to at this point.

Background

The Schedule Performance Index represents the relative amount that the task is behind or ahead of schedule. For example, if the task Build Fencehas a budget of $4,000 and the schedule performance index is 1.25, this would represent a task that is 25% ahead of schedule.

The underlying Planned Value (PV) and Earned Value (EV) must be calculated on a task by task basis and summed to determine the overall project’s SPI.

It must have a time point of reference, in other words, it is a “snapshot” at a certain point in time. If the project is currently active, the schedule performance index is changing. To put it another way, the project is getting more ahead or behind schedule as time goes on and as work goes on.

Schedule Baseline

In order to calculate the schedule performance index, the project must initially be divided into tasks and each task must be assigned the following data:

Start and Finish Dates

Budget

This is called the schedule baseline, and it gives the project manager something to track against. Project scheduling is one of the fundamental aspects of project management.

Planned Value (PV)

Also known as Budgeted Cost of Work Scheduled (BCWS), Planned Value is the amount of the task that is supposed to have been completed, in terms of the task budget. It is calculated from the project budget.

PV = Percent Complete (planned) x Task Budget

For example, if it’s Feb. 15 today, and the task is supposed to last from Feb. 10 to Feb. 20, it should be 50% complete. If the task budget is $4,000, PV = 50% x $4,000 = $2,000.

Earned Value (EV)

Also known as Budgeted Cost of Work Performed (BCWP), Earned Value is the amount of the task that is actually completed. It is also calculated from the project budget.

EV = Percent Complete (actual) x Task Budget

For example, if the actual percent complete is 75% and the task budget is $4,000, EV = 75% x $4,000 = $3,000.

Example

Let’s say we have a project with two tasks, building a fence and laying sod. The initial schedule baseline is:

The overall project schedule performance index is $3,300 / $2,690 = 1.23, which means that 23% more work has been accomplished than the project plan at this point. However, task 200 has an SPI of 0.43 which means that it is significantly behind schedule.

Related Earned Value Metrics

The Schedule Performance Index is usually analyzed in conjunction with the Cost Performance Index (CPI), which tells you how far over or under budget, rather than ahead or behind schedule, the project is.

SPI and CPI are both greater than 1.0: The project is ahead of schedule and under budget (hooray!)

SPI is greater than 1.0 and CPI is less than 1.0: The project is ahead of schedule but over budget. In other words, more tasks have been performed than were scheduled at this point, but the tasks that have been performed are over budget.

SPI is less than 1.0 and CPI is greater than 1.0: The project is under budget but behind schedule. In other words, less tasks have been performed than were scheduled at this point, but the tasks that have been performed are under budget.

SPI and CPI are both less than 1.0: The project is behind schedule and over budget (boo!)

The Schedule Variance (SV) is similar to SPI but tells you the absolute, rather than relative, amount the project is ahead or behind schedule.

About Bernie Roseke, P.Eng., PMP

Bernie Roseke, P.Eng., PMP, is the president of Roseke Engineering. As a bridge engineer and project manager, he manages projects ranging from small, local bridges to multi-million dollar projects. He is also the technical brains behind ProjectEngineer, the online project management system for engineers. He is a licensed professional engineer, certified project manager, and six sigma black belt. He lives in Lethbridge, Alberta, Canada, with his wife and two kids.